The present invention relates to a photoelectric conversion element and a method of using the same, an image sensor, and an optical sensor.
A conventional optical sensor is a device having photodiodes (PDs) formed in a semiconductor substrate made of, for example, silicon (Si) and a planar solid-state image sensor in which PDs are two-dimensionally arranged to read out signal charges generated in the respective PDs is widely used as the solid-state image sensor.
The structure in which color filters for transmitting light having specific wavelengths therethrough are disposed on the light incidence surface side of a planar solid-state image sensor is common in order to realize a color solid-state image sensor. At present, a single-plate solid-state image sensor which is widely used in a digital camera or other device and in which color filters for transmitting blue (B) light, green (G) light and red (R) light therethrough are regularly disposed on individual PDs in a two-dimensional array is well known.
The single-plate solid-state image sensor does not use light which did not pass through the color filters and hence suffers from poor light use efficiency. In recent years, the pixel size is decreasing with a view to increasing the number of pixels and there arise problems such as a decrease in aperture ratio and a decrease in light collection efficiency.
In order to solve these defects, a structure is known in which an amorphous silicon photoelectric conversion layer or an organic photoelectric conversion layer is formed on a substrate for reading out signals.
Several examples are known for the photoelectric conversion element, image sensor and optical sensor using the organic photoelectric conversion layer. Particularly in the photoelectric conversion element using the organic photoelectric conversion layer, the photoelectric conversion efficiency is to be improved while reducing the dark current. As the improvement methods, it is disclosed to introduce a p-n junction or a bulk heterojunction structure for the former purpose and to introduce a blocking layer for the latter purpose.
For instance, JP 2007-335760 A discloses a photoelectric conversion layer containing an acene compound which has high photoelectric conversion efficiency.